As long as it is DDR memory it will fit. Whether the G5 supports it is another story...

You may need those missing fans too, but I would ask someone who has used one that actually works. The last one I worked on was to be a motherboard swap. One stripped G5, one too recent G5 motherboard, and one iMac G5 motherboard later the guy finally bought a working used G5. He should have done that int he first place....